1. Field of the Invention
This invention relates to a heating apparatus such as microwave ovens in which food accommodated in a heating chamber is grouped into a first food group in which food contains a large volume of alcoholic component or a second food group in which food contains a small volume of alcoholic component and heating means is driven for a period of time in accordance with the grouped food group.
2. Description of the Prior Art
In conventional microwave ovens with an automatic cooking function, for example, it is determined whether a beverage to be heated is milk or Japanese sake which will hereinafter be referred to as "sake" when the beverage is warmed. A driving period of time of a magnetron is set on the basis of the result of determination. This manner of setting depends upon the difference of alcoholic concentration between the sake or milk. The alcoholic concentration is detected during a heating operation so that the food is determined to be sak/ or milk. A target temperature in heating the sake is normally set to be lower than one of the milk. When the weight of the sake is the same as that of the milk, a heating period of time of the sake is set to be lower than one of the milk. Accordingly, the time the presence or absence of alcohol is determined is set to be a time before the heating time period of the sake expires.
The presence or absence of alcohol is determined on the basis that a change rate of the alcoholic concentration in the heating chamber has reached a reference value at the above-mentioned time or a determination time. When the food to be heating is determined to be the sake at the determination time, a magnetron is driven until the heating time period of the sake expires. When the food cannot be determined to be the sake, the food is determined to be the milk and the magnetron is driven until the heating time period of the milk expires. Consequently, the food can be heated to a suitable temperature on the basis of the determination as to presence or absence of alcohol.
In the above-described prior art arrangement, however, presence or absence of alcohol in the beverage to be heated is determined only at one time during the heating operation. Accordingly, there is a possibility that an erroneous determination may result from the temperature in the heating chamber, the condition where the food has been stored in a refrigerator or the like, or the type of a receptacle containing the beverage such as the size of an opening of the receptacle through which the beverage is poured into and out of it. Since there are two kinds of foods in this case, that is, the sake and milk, the sake is excessively heating or the milk is insufficiently heated upon occurrence of the erroneous determination.